1. Field of the Invention
The present invention relates to a semiconductor device, in particular, to a semiconductor device including dual work function metal at the interface between high-k and base insulator.
2. Description of Related Art
Recently, a semiconductor device including a metal gate and high-k is becoming popular because the device can achieve a low current leakage. In order to obtain metal gate transistors having different threshold voltage, changing the work function of the gate for the transistors should be needed.
The following documents describe such technologies.
1) C. S. Park, M. M. Hussain, J. Huang, C. Park, K. Tateiwa, C. Young, H. K. Park, M. Cruz, D. Gilmer, K. Rader, J. Price, P. Lysaght, D. Heh, G. Bersuker, P. D. Kirsch, H.-H. Tseng, and R. Jammy, 2009 Symposium on VLSI Technology, 11A-1, p 208, (2009).
As shown in FIG. 2 in C. S. Park, after an AlOx cap and a hard mask are formed on a high-k, the hard mask and the AlOx cap are selectively removed. Then, a LaOx cap is formed on the high-k gate insulator and the hard mask. That is, the AlOx cap and the LaOx cap for work function metal are provided on the high-k.
2) Hirofumi Shinohara, Akira Katakami, Toshinari Watanabe, Manabu Hayashi, Satoshi Kamiyama, Yoshihiro Sugita, Takeo Matsuki, Takahisa Eimori, Jiro Yugami, Kazuto Ikeda, and Yuzuru Ohji, 2009 International Conference on SSDM, B-5-2, pp 789-790, (2009).
As shown in FIG. 1 in Hirofumi, Al2O3 and La2O3 for work function metal are also provided on a high-k gate insulator (HfO2).